Interaction of Climate and Atmospheric Chemistry through Dynamic Processes and Radiative Feedbacks

An atmosphere-ocean model including interactive atmospheric chemistry was used to quantify the importance of chemically induced radiative feedbacks on the climate sensitivity. Two types of initial radiative forcing were tested, the first one being caused by a CO2 concentration increased, the second one by enhanced emissions of surface NOx and CO emissions. Within this model framework, the most relevant chemical feedback (independent of the forcing type) is that induced by a modification of the ozone concentration distribution. It is a negative feedback that dampens the net impact of the initial radiative forcing. This effect is further enhanced as the ozone feedback modifies the feedback due to stratospheric water vapour. The climate sensitivity of the model is slightly reduced (by 5 to 10%), if chemically induced radiative feedbacks are accounted for. The relevance of chemical feedbacks increases with increasing initial radiative forcing. If the latter grows beyond a critical level (>10 W/m2), the role of chemical feedbacks becomes essential, because they avoid the occurrence of artificial non-physical interactions that may lead to a runaway greenhouse effect in the model system without interactive chemistry.